High molecular weight homo- or copolymers of ethylene oxide with a weight average molecular weight (MW) of 80,000 or more are water-soluble polymers which are often used to thicken aqueous solutions or to control diffusion, e.g., as a drug excipient. Lower molecular weight homo- or copolymers of propylene oxide or butylene oxide with a MW of 500 to 20,000 are typically used in polyurethane production, while polymers with a MW of 20,000-80,000 may be useful either in themselves or as intermediates in personal care or polymeric electrolyte applications. Ethylene oxide homo- or copolymers are generally made by heterogeneous catalysts which produce polymer with MW in the range of 2,000,000 to 20,000,000. Current processes for the production of polymer MW between 80,000 and 2,000,000 employ high-energy radiation to initiate radical chain scission in the polymer after it has left the reactor. This process is complex and costly, and may cause the polymer to become unstable and continue to lose molecular weight over time. What is needed is a new catalyst system which produces alkylene oxide homo- or copolymers, such as poly(ethylene oxide) (PEO) with a MW of 5,000 to 2,000,000 g/mol directly in the polymerization reactor.
The products of the reaction of hindered phenol ligands with aluminum compounds are known to catalyze the polymerization of alkylene oxides. The prior technologies are significantly deficient in either the range of polymer molecular weights or catalyst activity.
British Patent Specification GB 875161, to Petrochemicals Ltd., teaches the use of aluminum triphenoxide as a single-component catalyst for the polymerization of ethylene oxide. Catalyst activity is very poor.
Braune and Okuda (Angew. Chem. Int. Ed. 2003, 42, 64-68) describe how biphenolatoaluminum complexes, when combined with an anionic additive in substoichiometric quantities, are active catalysts for propylene oxide polymerization. Polymers with weight average molecular weights of less than 5,000 g/mol are obtained.
The published patent WO2002098559 A2, to Union Carbide, deals with the use of phenoxyaluminum complexes for the polymerization of ethylene oxide. Unfortunately, the catalyst activities disclosed in the Examples are not very high (<20 g(polymer)/mmol(Al)).
Chisholm and co-workers (Macromolecules 2001, 34, 8851-8857) discuss the uses of phenoxyaluminum complexes for the polymerization of propylene oxide. The catalysts are relatively inactive, having productivities of less than 5 g(polymer)/mmol(Al).
A paper by Kuran et al. (J. of Macromol. Sci., Pure Appl. Chem. 1998, A35, 427-437) describes the use of calixarene complexes of aluminum as catalysts for oxirane polymerization. Calixarenes are cyclic oligophenoxides. Reported polymer molecular weights are below 5,000 g/mol and total catalyst turnovers are less than 50.
A paper from Inoue and co-workers (Macromolecules 1994, 27, 2013-18) shows the use of Schiff-base aluminum complexes as catalysts for oxirane polymerization. Schiff bases contain phenol groups. Catalyst productivities and polymer molecular weights are fairly low (below 15 g(polymer)/mmol(Al) and below 30,000, respectively).
In a paper from Chisholm and co-workers (Inorg. Chem. 2004, 43, 7278-7280) the authors demonstrate the oligomerization of propylene oxide using a dinuclear chromium complex containing two Schiff-base coordination sites.
U.S. Pat. No. 3,186,958 to Hercules Powder Co. Ltd, teaches the use of combinations of trialkylaluminum compounds with substoichiometric levels of Lewis bases as catalysts for ethylene oxide polymerization. Reported catalyst productivities are below 10 g(polymer)/mmol(Al).
An article by Akatsuka et al. (Macromolecules 1994, 27, 2820-2825) describes the use of phenoxyaluminum complexes as cocatalysts for the polymerization of propylene oxide catalyzed by porphinatoaluminum complexes. The phenoxyaluminum species is not shown to be active by itself.
Ligands such as the ones described in the present patent application are disclosed by Cottone and Scott (Organometallics 2000, 19, 5254-5256). In this paper ligands are shown which bind two aluminum atoms which can coordinate a chloride ion between them. No catalysis is reported using the complexes. In oral presentations in the years 1999 and 2000, members of this research group reported that complexes of tetraphenols possessing two aluminum atoms are active for the catalysis of monomeric molecular reactions involving carbonyl group transformations (see: Cottone, A.; Scott, M. J. Book of Abstracts, 218th ACS National Meeting, New Orleans, Aug. 22-26, 1999, INOR-192; Cottone, A., III; Scott, M. J. Book of Abstracts, 219th ACS National Meeting, San Francisco, Calif., Mar. 26-30, 2000, INOR-208; Scott, M. J.; Cottone, A., III; Lecuivre, J. L. Book of Abstracts, 219th ACS National Meeting, San Francisco, Calif., Mar. 26-30, 2000, INOR-421; Cottone, A., III; Scott, M. J. Abstracts of Papers, 220th ACS National Meeting, Washington, D.C., United States, Aug. 20-24, 2000, INOR-031).
U.S. Pat. No. 3,607,785 A to Institut Francais du Petrole des Carburants et Lubrifiants, teaches the polymerization of alkylene oxides using bimetallic catalysts. The bimetallic catalyst is produced by reacting a trivalent metal compound (R1O)2M′-OX with a compound of a divalent metal Y—O-M-Z, wherein M′ is aluminum, M is zinc, Z is a hydrocarbyl acyloxy radical, X is R4, Y is a hydrocarbon, and R1 to R4 are hydrocarbon monovalent radicals.
References to the acceleration of organic reactions due to the binding of one ligand with more than one metal exist, but none deal with the polymerization of oxiranes. These include the work of Ooi and co-workers (J. Am. Chem. Soc. 2004, 126, 1150-1160). The following reference discloses the use of bis-Schiff base ligands which bind two aluminum atoms as catalysts for cyclic lactone and carbonate polymerization: Yang et al., J. Polym. Sci. A.: Polym. Chem. 2005, 43, 373-384.
In view of the low activities of the catalysts which are known for ethylene oxide polymerization, there is a need for high-activity catalysts for the homo- or polymerization of alkylene oxides.